Autumn Sea Surface Temperature Research Articles

Synergistic effect of boreal autumn SST over the tropical and South Pacific and winter NAO on winter precipitation in the southern Europe

We find a positive phase of meridional tripole pattern of boreal autumn sea surface temperature anomalies over the tropical and South Pacific (TSPT+ ) has a synergistic effect with winter negative NAO (NAO−) on the amplitude and occurrence of winter precipitation in southern Europe (SEWP). This synergistic effect is attributed to the linear superposition and nonlinear effect of winter NAO− and preceding autumn TSPT+ . The autumn TSPT+ can persist into winter, and the winter TSPT+ with NAO− can stimulate a greater amount of Rossby wave energy propagating to the North Atlantic-Europe (NAE) region than without NAO−, and thereby synergistically regulating circulation with winter NAO−. Thus, winter NAO− and autumn TSPT+ have a synergistic effect on the northwest-southeast trending positive-negative-positive winter circulation over the NAE region. Driven by the intensified mean circulation, water vapor transports and storm activity over southern Europe are evidently strong, which is in favor of SEWP formation.

Interannual variation of the number of winter extreme low temperature days in southern China and influencing factors

The interannual variation of the number of winter extreme low temperature days (NELTD) in southern China from 1980 to 2019 is analyzed, and the individual and combined effects of the autumn sea surface temperature anomaly (SSTA) in the central equatorial Pacific and Siberian snow cover extent anomaly (SCEA) are investigated. The analysis shows that the anomalous atmospheric circulation in Eurasia is dominated by the meridional dipole pattern with the characteristic of “high north and low south” during the winter with large NELTD in southern China. The autumn SSTA in the central equatorial Pacific influences the winter NELTD mainly through the anomalous atmospheric circulation at the mid–low latitudes while the Siberian SCEA in October acts by affecting that at the mid–high latitudes. A cold SSTA is conducive to strengthening the winter East Asian trough and subtropical jet, as well as abnormal northeasterly wind in most parts of southern China. However, the central equatorial Pacific SSTA has a limited influence on the Ural ridge, polar front jet, and Siberian High at the mid–high latitudes. On the other hand, the Siberian SCEA could result in anomalous atmospheric circulation at the mid–high latitudes, which has a strengthening and supplementing effect on that of SSTA in the central equatorial Pacific. During the winter following the negative SCEA in October, the Ural ridge and Siberian High are strengthened while the polar front jet is weakened. The anomalous atmospheric circulation in Eurasia is dominated by a meridional dipole pattern of “high north and low south”. The comparative analysis reveals that both SSTA and SCEA play an important role in the NELTD in southern China, but they are independent factors and act in different ways. Therefore, the combined effect of autumn SSTA in the central equatorial Pacific and Siberian SCEA could contribute to the prediction of the winter NELTD in southern China.

Recent marine growth declines in wild and ranched Atlantic salmonSalmo salarfrom a western European catchment discovered using a 62-year time series

AbstractTo address population declines, many salmon populations are supplemented with hatchery-bred fish. Little is known about how growth performance of hatchery-bred and wild salmon compare during critical periods such as the first summer at sea. This study compares scale growth measurements between 1725 ranched and 1976 wild salmon from the Burrishoole catchment (western Ireland) over 62 years (1956–2017). Post-smolt growth (PSG) was greater in wild than ranched fish; this difference was consistent with compensatory growth rather than size-dependant growth. Temporal trends in marine growth of wild and ranched fish were similar, with a marked decline in PSG and return size after the early 2000s. The decline in PSG was significantly related to freshwater growth and autumn sea surface temperature in the Norwegian Sea. Temporal changes in the pattern of intercirculi spacings along the PSG growth trajectory were also identified; circuli deposited during the first summer at sea were narrower in the 2000s and 2010s compared to earlier decades, while circuli from the first winter were wider. The recent decline in growth affects both populations similarly, is associated with increasing temperature and is manifested as a change in growth pattern as well as overall growth.

Impact of the climate regime shift around 2000 on recruitment of Antarctic krill at the Antarctic Peninsula and South Georgia

We examined how the climate regime shift around 2000 affected Antarctic krill recruitment variability at the North Antarctic Peninsula (NAP) and South Georgia (SG) during the period of 1990s through to 2000s. We used sea surface temperature (SST) as a proxy of the monthly sea ice extent and related it to the recruitment index (proportion of 1-year-old krill) of each succeeding year for NAP and SG by examining the correlation of the time series before and after 2000. For NAP, recruitment index was negatively correlated with winter SST at NAP in the 1990s but with autumn SST in the 2000s, suggesting that good recruitment was supported by extensive winter sea-ice in the 1990s but by extensive autumn sea-ice in the 2000s. This was attributed to the regime shift featured by winter warming and autumn cooling after 2000. For SG, recruitment was negatively correlated with winter SST at NAP in the 1990s but positively correlated with autumn SST in the southern Scotia Sea (SSS) in the 2000s. According to particle tracking experiment from NAP to SG in relation to the sea-ice extent and position of SACCF (Southern Antarctic Circumpolar Current Front), less sea-ice extent in 2000s meant less larvae distributing as north as SACCF, resulting in much fewer larval being transported to SG. Hence, we hypothesized that the regime shift weakened the connection between NAP and SG, but instead SSS became the main driver of recruitment at SG. We presume the krill population demonstrated adaptability to the regime shift by offsetting the unfavorable winter condition with the favorable autumn condition at NAP and for SG, replacing the source of recruits with those closer to it.

Responses of East Asian Climate to SST Anomalies in the Kuroshio Extension Region during Boreal Autumn

Abstract Sea surface temperature anomalies (SSTAs) in the Kuroshio Extension (KE) region play a key role in influencing midlatitude climate variations. This study investigates the impacts of SSTAs in the KE region (KE-SSTA) on East Asian climate during boreal autumn. The results reveal that positive KE-SSTA, changing the meridional temperature gradient in the lower troposphere, contributes to the formation of an anomalous quasi-barotropic anticyclonic circulation (AC) over the KE region. Such a configuration tends to be affected by wind through thermal wind adjustment. Simultaneously, it is also impacted by eddy activity related to the strengthened atmospheric baroclinicity through transient eddy feedback. By both means, obvious descending motion and warm advection are generated, which increases tropospheric temperature through adiabatic heating and further maintains the abnormal AC over the KE region. This anomalous circulation changes wind in the east of the East Asian trough, which favors the transportation of warm and wet air from the midlatitude northwest Pacific and further causes the increase of temperature in northeastern East Asia. Moreover, it also leads to the convergence and divergence of water vapor fluxes in Northeast Asia and eastern North China, favoring the increase and decrease of precipitation in the two regions, respectively. The above responsive characteristics of the midlatitude atmospheric circulation to positive KE-SSTA can be confirmed by numerical experiments. These results suggest that anomalous SST in the KE region can be used as a potentially effective predictability source for autumn climate variations in the mid- to high latitudes of East Asia. Significance Statement Anomalous variations of sea surface temperature (SST) in the Kuroshio Extension (KE) region play an essential role in influencing midlatitude climate variations. Considering the importance of autumn climate in East Asia to agricultural production, this study aims to explore the relationship between the East Asian climate and autumn SST anomaly in the KE region (KE-SSTA), and to understand how KE-SSTA effects East Asian climate during boreal autumn. Our results suggest that KE-SSTA can be used as one of the effective predictors of East Asian climate, which will contribute to the improvement of short-term climate prediction levels over East Asia.

Interannual variability of winter precipitation over the Lambert Glacier basin linked to the dipole pattern of sea surface temperature in the southern Indian Ocean

Variations in annual accumulated snowfall over the Antarctic ice sheet have a significant and direct impact on mean sea-level change. The interannual variability of the precipitation over coastal Antarctica adjacent to the southern Indian Ocean (SIO) cannot be totally explained by the dominant mode of atmospheric variability in the Southern Hemisphere. This study explores the possible contributions from sea surface temperature (SST) anomalies in SIO on the precipitation over East Antarctica. The results suggest that the winter precipitation in the Lambert Glacier basin (LGB) is closely related to the autumn SST variability in SIO without the influence of El Niño–Southern Oscillation. It is shown that the positive autumn SIO dipole (SIOD) of SST anomalies is usually followed by reduced precipitation in the following winter over the LGB region and vice versa. The positive (negative) autumn SIOD can persist into the winter and excite cyclonic (anticyclonic) circulation and deepen (weaken) SIO low in high latitude, corresponding to an enhanced northward (southward) wind anomaly in LGB and central SIO. This mechanism prevents (promotes) the transportation of warm and moist marine air to the LGB region and hence decreases (increases) the precipitation during the following winter.

Influences of different intensities of El Niño–Southern Oscillation on South American precipitation

AbstractEl Niño–Southern Oscillation (ENSO) phenomena occur in the equatorial Pacific and differentially affect the global climate. Recently, studies have begun to analyse the influence of ENSO intensity on the global climate, but how this intensity affects South American precipitation remains unclear. This work defined the ENSO intensities each season (versus annually, as is more commonly done) because understanding this seasonal intensity is essential for seasonal forecasting. The atmospheric patterns identified in this study showed that the stronger the sea surface temperature (SST) anomalies (SSTA) in the equatorial eastern Pacific were, the stronger the atmospheric responses. The known South American precipitation pattern occurred at all ENSO intensity categories but had different intensities. However, the most important patterns in this study differed from the main pattern. Central‐eastern South America did not have a notable precipitation pattern during all El Niño (EN) years, but there was a negative pattern of strong ENs. In addition, the intensity of the precipitation anomaly during weak EN and La Niña (LN), mainly in northeastern South America, was stronger in austral autumn than in austral summer because the intensity in a previous season can influence the current season's precipitation pattern and the total SST in autumn is stronger than that in summer. Asymmetries between EN and LN events are important to consider; EN tends to be more intense than LN, and deep convection anomalies during EN are displaced eastward relative to those during LN. In this study, categories were defined based on ENSO intensities, but asymmetries appeared in atmospheric patterns, mainly in omega patterns during strong events. The intensities of SSTAs over the equatorial eastern Pacific affected the intensities of the Walker circulation and Rossby waves and, consequently, the intensity of precipitation patterns in different South American regions.

On an Improved Second‐Moment Closure Model for Langmuir Turbulence Conditions and Its Application

AbstractRecently, a k‐ω second‐moment closure (SMC) model including the Langmuir turbulence effects was proposed by Yu et al. (2018, https://doi.org/10.1029/2018jc013878), however, the equations for determining the stability functions in it are very complicated. In this study, the equations of the stability functions are derived in more detail and a new explicit version is proposed. In the meantime, a new constant cω4 = 0.15 is introduced into the turbulent frequency transport equation to manifest the role of the shear generating term caused by the Stokes drift. And then the performance of the new SMC model is investigated by one‐dimensional Papa Ocean Station simulation and three‐dimensional global climate model simulation. The results show that the use of the new SMC model produces significant changes in the results of the ocean surface boundary layer simulations at the Papa Ocean Station, especially for the summer and autumn sea surface temperature (SST) simulations, and for the mixed layer depth (MLD) and mixed layer temperature (MLT) in the mixed layer deepening process. In the three‐dimensional simulation, the new SMC model resulted in a decrease of more than 34% in the annual root mean square error of SST in the northern extratropical region compared to the non‐LT effects model. The simulated MLD for tropical regions in winter and summer has also improved by 61.9% and 53.6%, respectively. The effect of the new SMC model on the MLT is mainly found in the regions beyond the tropical in summer and the tropical and northern extratropical regions in winter.

Roles of climate variability on the rapid increases of early winter haze pollution in North China after 2010

Abstract. North China experiences severe haze pollution in early winter, resulting in many premature deaths and considerable economic losses. The number of haze days in early winter (December and January) in North China (HDNC) increased rapidly after 2010 but declined slowly before 2010, reflecting a trend reversal. Global warming and emissions were two fundamental drivers of the long-term increasing trend of haze, but no studies have focused on this trend reversal. The autumn sea surface temperature (SST) in the Pacific and Atlantic, Eurasian snow cover and central Siberian soil moisture, which exhibited completely opposite trends before and after 2010, might have close relationships with identical trends of meteorological conditions related to haze pollution in North China. Numerical experiments with a fixed emission level confirmed the physical relationships between the climate drivers and HDNC during both decreasing and increasing periods. These external drivers induced a larger decreasing trend of HDNC than the observations, and combined with the persistently increasing trend of anthropogenic emissions, resulted in a realistic, slowly decreasing trend. However, after 2010, the increasing trends driven by these climate divers and human emissions jointly led to a rapid increase in HDNC.

Long-term observations of pteropod phenology along the Western Antarctic Peninsula

Shifts in phenology – annually occurring life history events – have been observed among many marine organisms due to global warming. We examined if phenological changes in the pteropod (pelagic snail) Limacina helicina antarctica have occurred along the Western Antarctic Peninsula, one of the most intensely warming regions on Earth, which would have important implications for regional food web dynamics. Pteropod shell diameters were analyzed from samples collected in the Palmer Antarctica Long-Term Ecological Research (PAL LTER) program year-round sediment trap from 2004 to 2018. There was considerable interannual variability in the time of appearance of a new pteropod cohort, which ranged from day of year 22–255, but no long-term, directional change. Mean L. h. antarctica growth rate for the time series was 0.009 mm day−1 and there was no significant long-term change in growth rate. This study represents the first in the Southern Ocean to illustrate that pteropods actively grow throughout the winter season. Sea ice was the dominant driver of pteropod phenology, with earlier sea ice retreat the year prior, lower winter sea surface temperature (SST) the year prior, and higher primary productivity in the same year leading to earlier pteropod time of appearance. Similarly, more open water with higher autumn SST, both the year prior, and elevated chlorophyll a the same year, promoted faster pteropod growth. These results indicate that while pteropods are responsive to considerable environmental variability, their phenology has remained relatively stable. The identified responses of pteropod phenology to environmental shifts are key for determining future effects of climate change on biogeochemical cycling and plankton trophic interactions in the region.

Analyzing the Effects of Sea Surface Temperature (SST) on Soil Moisture (SM) in Coastal Areas of Eastern China

In this paper, we applied the re-analysis data cobe-SST (cobe-sea surface temperature) and Global Land Data Assimilation System (GLDAS) surface soil moisture (SM) data from 1961 to 2011 by using regional correlation analysis and time series causality analysis to trace annual variations in and identify the abnormal relationship of sea surface temperature (SST) in the eastern China Sea and SM in eastern China (EC). We also used satellite Moderate Resolution Imaging Spectroradiometer (MODIS) SST and AMSR-E SM data to examine the correlation of SST and SM in EC from 2004–2009. The results show that the SST in the eastern China Sea has experienced a warming trend since 1987, whereas the SM in EC has shown a drying trend since 1978. Before 1967 and after 1997, SST and SM changed during opposite phases, whereas from 1967 to 1997 they changed during the same phase. The differences between them may result from the abnormal summer precipitation causing abnormal SM. According to the regional correlation analysis, SST of the East China Sea is significantly related to SM in the southeast coastal area, and temporal sequence causality analysis shows that SST is correlated with and has higher influence on SM than vice versa. SM during spring and autumn shows a similar correlation with SST during the four seasons, so that SM in spring and autumn is positively correlated with SST in autumn and negatively correlated with SST in other seasons. SM in summer and winter correlated with SST in the four seasons, contradicting the foregoing conclusions. All these findings indicate that the thermodynamic state of the eastern China Sea has affected SM in EC.

Evaluation of environmental proxies based on long chain alkyl diols in the East China Sea

Long chain alkyl diols (LCDs) in marine environments are useful indicators of source organisms, ambient temperature, upwelling and nutrient conditions. However, the distribution of LCDs in the western Pacific marginal seas has been rarely reported, where wide shallow continental shelves and huge freshwater input from many rivers occur. In this study, we analyzed LCDs in surface sediments distributed from the Changjiang River estuary (CRE) to the East China Sea shelf to evaluate their sources and associated environmental proxies. Our results showed that the fractional abundance of C32 1,15-diol (FC32 1,15-diol) was highest in coastal area close to the CRE, with FC32 1,15-diol > 15% implying significant freshwater input. The C28 and C30 1,13-diols showed a similar spatial distribution to the C32 1,15-diol, suggesting that the long chain diol index (LDI), a sea surface temperature (SST) proxy, may be biased by freshwater-derived diols. By excluding the freshwater-influenced samples (i.e., FC32 1,15-diol > 15%), LDI reflected the autumn SST, yielding minimum temperature residuals (0.2 ± 1.5 °C). The C28, C30 and C30:1 1,14-diols were abundant in the mid-depth (15–45 m) offshore environment that was affected only slightly by the Changjiang River plume, and decreased toward both the eutrophic estuarine and oligotrophic marine environments; whereas the C28:1 1,14-diol showed higher fractional abundances close to the CE. The spatial distribution of 1,14-diols is similar to that reported for Proboscia diatoms in this region, although the exact sources of 1,14-diol requires further study. Nutrient proxies based on 1,14-diols did not correlate well with nutrient concentrations in this river-dominated marginal sea, where nutrient supply is dominated by the Changjiang River input.

Predicting wintertime windy days in Beijing with the preceding autumn sea surface temperature and large-scale circulation patterns

In this study, we investigate the role of sea surface temperature and large-scale circulation patterns in the preceding autumn for the prediction of wintertime windy days in Beijing during the period of 1979–2016, based on a time-scale decomposition approach. A windy day is defined according to the threshold of 2 m·s−1, which can effectively remove or reduce air pollution of Beijing. Wintertime windy days in Beijing, preceding autumn sea surface temperature and large-scale climate indices are separated into the interannual and interdecadal components. For the interannual component, the preceding autumn sea surface temperature in central western Pacific Ocean, Polar/Eurasia pattern, and Scandinavia pattern are identified as predictors of wintertime windy days in Beijing. For the interdecadal component, the identified predictors include the preceding autumn sea surface temperature in northeastern part of North Atlantic Ocean, Arctic Oscillation, and North Atlantic Oscillation. We develop statistical models for the interannual and interdecadal components based on these preceding autumn predictors, and take them together to predict wintertime windy days in Beijing. The leave-one-out cross-validation for 1979–2016 time series shows that 76% of the total variance of observed wintertime windy days in Beijing can be predicted. Hindcast experiments for the period of 1999–2016 also yield the high prediction skills. The physical mechanisms responsible for links between these predictors and wintertime windy days in Beijing are also discussed. The statistical models proposed herein are expected to be applied to and aid to improve seasonal forecasting of wintertime windy days in Beijing.

A statistical forecast model for the Chinese winter temperature based on autumn SST anomalies

This study investigates the impacts of the autumn sea surface temperature anomalies (SSTAs) on the following winter (December-January-February, DJF) 2-m air temperature anomalies (TSAs) in China and discusses the potential predictability of the DJF TSAs based on the intimate link between the DJF TSAs and autumn global SSTAs. The empirical orthogonal function (EOF) analysis suggests that the three leading EOF modes jointly account for 80% of the total TSA variances and are characterized by homogeneous spatial, north-south seesaw, and cross-structure patterns. These EOFs are temporally stable and suggest the potential predictability of the DJF TSAs. The EOF1 mode is influenced by changes in the intensities of the Siberian high, East Asian winter monsoon (EAWM), and East Asian trough related to a Eurasian teleconnection pattern, which can be tracked back to the autumn (September-October-November, SON) SSTAs. The Arctic oscillation (AO) exerts a strong influence on the EOF2 mode. The configuration of the global SON SSTAs induces the AO signal and causes a TSA oscillation between the northern and southern parts of China. The EOF3 mode is associated with the western pathway of the EAWM and the westward shift of the Siberian high, which are attributed to two SON SSTA patterns. The multiple correlation coefficients between the SSTA indices and winter atmospheric circulations suggest the cooperative contribution of the autumn global SSTAs to the DJF TSAs. Therefore, a physically motivated statistical model is established based on the autumn SSTA indices. Cross-validation suggests that this statistical forecast model shows a good performance in predicting the DJF TSAs.

Large‐scale indices for assessing typhoon activity around Taiwan

This study quantifies large‐scale indices associated with variations in the western Pacific subtropical high (WPSH) and tropical sea surface temperature (SST) to assess typhoon activity around Taiwan. A WPSH index is constructed for both summer and early autumn as the meridional difference of areal means between the northern (120°–130°E, 25°–30°N) and southern (120°–130°E, 20°–25°N) regions (north minus south) of the 500 hPa height. These are regions north and south of Taiwan. In the high index years, typhoons forming in the tropical western North Pacific tend to be steered by easterly/southeasterly flows at the southwestern boundary of a northwards‐shifted WPSH to move northwestwards towards Taiwan, leading to increased typhoon activity around Taiwan. In the low index years, a southwards‐shifted, eastwards‐retreated WPSH steers typhoons along its western periphery to move northwards away from Taiwan. The northwards shift of the WPSH and consequent enhanced typhoon activity around Taiwan associate with a meridional wave train induced by a zonal SST gradient in summer, but link with a Matsuno‐Gill‐type response induced by tropical SSTs in early autumn. As so, the summer SST index is defined as a zonal gradient of areal‐mean SSTs between the tropical western Pacific (150°–175°E, 10°–20°N) and the Bay of Bengal–South China Sea–Philippine Sea region (80°–130°E, 5°–20°N) (former minus latter). In early autumn, the SST index is averaged from the tropical western Pacific over 130°–165°E, 5°S–5°N. All WPSH and SST indices in summer and early autumn are significantly correlated (at the 99% level) with the number of typhoons affecting Taiwan.

A Comparison of Late Quaternary Organic Proxy-Based Paleotemperature Records of the Central Sea of Okhotsk.

The long‐chain diol index (LDI) is a new organic sea surface temperature (SST) proxy based on the distribution of long‐chain diols. It has been applied in several environments but not yet in subpolar regions. Here we tested the LDI on surface sediments and a sediment core from the Sea of Okhotsk, which is the southernmost seasonal sea ice‐covered region in the Northern Hemisphere, and compared it with other organic temperature proxies, that is, U37k′ and TEXL 86. In the surface sediments, the LDI is correlated with autumn SST, similar to the U37k′ but different from the TEXL 86 that correlates best with summer sea subsurface temperature. Remarkably, the obtained local LDI calibration was significantly different from the global core‐top calibration. We used the local LDI calibration to reconstruct past SST changes in the central Sea of Okhotsk. The LDI‐SST record shows low glacial (Marine Isotope Stage, MIS 2, 4, and 6) and high interglacial (MIS 1 and MIS 5) temperatures and follows the same pattern as the U37k′‐SST and a previously published TEXL 86 temperature record. Similar to the modern situation, the reconstructed temperatures during the interglacials likely reflect different seasons, that is, summer for the TEXL 86 and autumn for U37k′ and LDI. During glacials, the reconstructed temperatures of all three proxies are similar to each other, likely reflecting summer temperatures as this was the only season free of sea ice. Our results suggest that the LDI is a suitable proxy to reconstruct subpolar seawater temperatures.

East Asian winter monsoon forecasting schemes based on the NCEP’s climate forecast system

The East Asian winter monsoon (EAWM) is the major climate system in the Northern Hemisphere during boreal winter. In this study, we developed two schemes to improve the forecasting skill of the interannual variability of the EAWM index (EAWMI) using the interannual increment prediction method, also known as the DY method. First, we found that version 2 of the NCEP’s Climate Forecast System (CFSv2) showed higher skill in predicting the EAWMI in DY form than not. So, based on the advantage of the DY method, Scheme-I was obtained by adding the EAWMI DY predicted by CFSv2 to the observed EAWMI in the previous year. This scheme showed higher forecasting skill than CFSv2. Specifically, during 1983–2016, the temporal correlation coefficient between the Scheme-I-predicted and observed EAWMI was 0.47, exceeding the 99% significance level, with the root-mean-square error (RMSE) decreased by 12%. The autumn Arctic sea ice and North Pacific sea surface temperature (SST) are two important external forcing factors for the interannual variability of the EAWM. Therefore, a second (hybrid) prediction scheme, Scheme-II, was also developed. This scheme not only involved the EAWMI DY of CFSv2, but also the sea-ice concentration (SIC) observed the previous autumn in the Laptev and East Siberian seas and the temporal coefficients of the third mode of the North Pacific SST in DY form. We found that a negative SIC anomaly in the preceding autumn over the Laptev and the East Siberian seas could lead to a significant enhancement of the Aleutian low and East Asian westerly jet in the following winter. However, the intensity of the winter Siberian high was mainly affected by the third mode of the North Pacific autumn SST. Scheme-I and Scheme-II also showed higher predictive ability for the EAWMI in negative anomaly years compared to CFSv2. More importantly, the improvement in the prediction skill of the EAWMI by the new schemes, especially for Scheme-II, could enhance the forecasting skill of the winter 2-m air temperature (T-2m) in most parts of China, as well as the intensity of the Aleutian low and Siberian high in winter. The new schemes provide a theoretical basis for improving the prediction of winter climate in China.

Role of atmospheric circulations in haze pollution in December 2016

Abstract. In the east of China, recent haze pollution has been severe and damaging. In addition to anthropogenic emissions, atmospheric circulations and local meteorological conditions were conducive factors. The number of December haze days over North China and the Huanghuai area has increased sharply since 2010 and was greatest in 2016. During 2016, the most aggressive control measures for anthropogenic emissions were implemented from 16 to 21 December, but the most severe haze pollution still occurred, covering approximately 25 % of the land area of China and lasting for 6 days. The atmospheric circulations must play critical roles in the sub-seasonal haze events. Actually, the positive phase of the East Atlantic–West Russia pattern in the middle troposphere strengthened the anomalous anti-cyclone over the NH area that confined vertical motion below. The associated southerly anomalies made the cold air and surface wind speed weaker, but enhanced the humid flow. Thus, the horizontal and vertical dispersion of atmospheric particulates was suppressed and the pollutants gathered within a narrow space. In December 2016, these key indices were strongly beneficial for haze occurrence and combined to result in the severest haze pollution. The influences of the preceding autumn sea surface temperature near the Gulf of Alaska and the subtropical eastern Pacific, October–November snow cover in western Siberia, and associated physical processes on haze pollution are also discussed.

Partial least regression approach to forecast the East Asian winter monsoon using Eurasian snow cover and sea surface temperature

Seasonal prediction of the East Asian (EA) winter monsoon (EAWM) is of great significance yet a challenging issue. In this study, three statistical seasonal prediction models for the EAWM are established using three leading modes of the Eurasian snow cover (ESC), the first leading mode of sea surface temperature (SST) and the four leading modes of the combination of the ESC and SST in preceding autumn, respectively. These leading modes are identified by the partial-least square (PLS) regression. The first PLS (PLS1) mode for the ESC features significantly anomalous snow cover in Siberia and Tibetan Plateau regions. The ESC second PLS (PLS2) mode corresponds to large areas of snow cover anomalies in the central Siberia, whereas the third PLS (PLS3) mode a meridional seesaw pattern of ESC. The SST PLS1 mode basically exhibits an El Nino-Southern Oscillation developing phase in equatorial eastern Pacific and significant SST anomalies in North Atlantic. A strong EAWM tends to emerge in a La Nina year concurrent with cold SST anomalies in the North Atlantic, and vice versa. After a 35-year training period (1967–2001), three PLS seasonal prediction models are constructed and the 11-year hindcast is performed for the period of 2002–2012, respectively. The PLS model based on combination of the autumn ESC and SST exhibits the best hindcast skill among the three models, its correlation coefficient between the observation and the hindcast reaching 0.86. This indicates that this physical-based PLS model may provide another practical tool for the EAWM. In addition, the relative contribution of the ESC and SST is also examined by assessing the hindcast skills of the other two PLS models constructed solely by the ESC or SST. Possible physical mechanisms are also discussed.

Impact of the Barents Sea SST in Autumn on the Winter Climate in Northeast China

We studied effects of sea surface temperature anomaly (SSTA) in the Barents Sea in autumn on the atmospheric circulation in northeast China in winter, using the NCEP reanalysis data and sea surface temperature (SST) data of the Hadley Center. The results show that the ocean thermal conditions in the Barents Sea in autumn can be used as an important reference factor for predicting the cold air activity in China. When the sea surface temperature anomaly of the Barents Sea elevated in the autumn, the sea-level pressure anomaly elevated in eastern China on December, northeast China and southeastern Russia on January and February. In the years when the SSTA of the Barents Sea elevated in the autumn, the abnormal high-pressure ridge developed over Europe, and the geopotential height in western China appeared negative anomaly at 500 hPa. At 1000 hPa, the Mongolia high-pressure increased and the northerly airflow strengthened the cold high-latitude air broke out to the south, which was easy to affect northeast and north of China. In negative SSTA years, the high-pressure ridge was west to the north Atlantic, and the geopotential height in central and northern Siberia appeared negative anomaly at 500 hPa; the Mongolia high-pressure was weakened at 1000 hPa.